Both of pop superstar Michael Jackson's arms were scarred with track marks, investigators probing his death say, and the marks are consistent with the finding of the potent sedative propofol (trade name Diprivan) in his home -- a drug that is increasingly at the center of their probe into what caused Jackson's death, ABC News has learned.

According to sources involved in the death investigation, several Hollywood and Beverly Hills doctors are now part of the investigation.

in cooperation with the Drug Enforcement Administration. The California Department of Justice has offered technical support in terms of its powerful searchable data base of patient information that includes drugs, doses, the doctors that administered them and the patients that received them.

Prescription medications were found inside Jackson 's $100,000 per month rental home that included ones in his name and ones in other names, including ones that appeared to investigators to be aliases. The medications had been prescribed by multiple doctors.

Jackson was addicted to the analgesic Demerol and to Oxycontin, investigators have told ABC News, and took the drugs daily. Medical experts have reported propofol "blocks out the world."

Those addicted to it routinely report that their abuse began with using the drug to treat insomnia -- an ongoing problem for Jackson.

Medical experts point out that the abuse of Demerol could have set the stage for cardiac arrest, by increasing Jackson 's risk.

One pharmacologist blogged about Propofol this week and explained in his science blog how Demerol abuse could have caused cardiac problems and could have increased his risk for heart rhythm disturbances from the Propofol: "As I wrote last week in my blog post on Demerol ® (meperidine), Jackson's reported long-term use of this analgesic for back pain may have already primed him for cardiac problems due to the accumulation of a toxic metabolite, normeperidine," Dr. David Kroll said. "However, most relevant to the Jackson case is that propofol can cause cardiac tachyarrhythmias (rhythmic disturbances at high heart rate), especially in people predisposed to cardiac problems."

Drugs Found in Michael Jackson's Home

Medical experts contacted by the ABC News Medical Unit said that the list of 20 drugs reportedly found in Jackson's rented home was "jaw-dropping" and "amazing."

"That list is enough to put down a swarm of zombies," said Richard Bradley, Chief, Division of EMS and Disaster Medicine at the University of Texas Health Science Center at Houston.

"The list …would be typical for an anesthesia cart in an operating room or what you might find in a recovery room, ICU, ED, etc.. Definitely not what you'd expect to find in a home," said Joseph Ornato, Chair of the Department of Medicine at Virginia Commonwealth University.

ABC News has reported on a number of those drugs including Demerol and Oxycontin, which the experts note are "cousins to morphine."